1. Field of the Invention
The present invention relates to a zoom lens system, and more particularly, to a zoom lens system suitable for an image pickup apparatus such as a digital still camera or a video camera.
2. Description of the Related Art
The zoom lens systems for use in digital cameras, digital video cameras, and the like have been demanded to provide a wide field angle, a high zoom ratio, a compact size, and a high optical performance.
In cameras (image pickup apparatus) each using a solid-state image pickup element, diverse optical members such as a low-pass filter or a chromatic correction filter are disposed between a lens end portion and the solid-state image pickup element. For that reason, the zoom lens systems used in those image pickup apparatuses have been demanded to provide a long back focus. Further, in order to prevent color shading, the zoom lens systems have been demanded to provide an excellent telecentric characteristic on an image side.
As an optical system configured to easily ensure the back focus, there is a negative-lead zoom lens system in which a lens unit with a negative refractive power is disposed closest to the object side.
A zoom lens system has been known which is downsized and telecentric on the image side, and includes a first lens unit with a negative refractive power, a second lens unit with a positive refractive power, and a third lens unit with the positive refractive power arranged in order of from the object side toward the image side (U.S. Pat. No. 6,822,808, U.S. Pat. No. 6,498,687, Japanese Patent Application Laid-Open No. 2004-61675, U.S. Pat. No. 7,333,275, U.S. Pat. No. 7,215,483, U.S. Pat. No. 7,113,347, U.S. Pat. No. 7,295,381).
In order to obtain a high optical performance high in the entire zoom range while downsizing the entire system in the zoom lens system including those three units, it is important to appropriately set the lens configurations of the respective lens units.
In particular, it is important to appropriately set the configuration and material of the respective lenses that constitute the first lens unit so as to reduce a variation in various aberrations caused by zooming.